1. Field of the Invention
The present invention relates to a rotary connector used as electrical connection means for providing a heater device incorporated in a steering apparatus of a motor vehicle or the like and an electronic device such as an air bag system equipped on a car body with an electrical connection.
2. Description of the Related Art
A rotary connector is generally incorporated in a steering apparatus of a motor vehicle or the like and employed as electrical connection means for providing a heater circuit employed in a steering apparatus, an air bag circuit, a horn circuit or other switch circuits, all of which are incorporated in a steering wheel, with an electrical connection. Furthermore, the rotary connector basically comprises a pair of a stationary housing and a movable housing, both being disposed coaxially and connected together so as to be rotatable relatively to each other, an annular space as a cable housing formed between a pair of those stationary and movable housings, a flexible cable housed in the annular space in a manner that the flexible cable can be wound and unwound, and lead blocks correspondingly connected to both ends of the flexible cable.
The flexible cable is constructed so that a plurality of (for example, four pieces of) conductors made of a flat strip of extremely thin copper foil or the like, each conductor being interposed between two sheets of insulating films as a flat strip of base film, are disposed in parallel with each other and stuck to the insulating films.
The rotary connector having such basic construction is further fabricated as follows: fix the stationary housing to the car body while fixing the movable housing to the handle member; and further, connect both ends of the flexible cable to associated electronic devices on the sides of the car body and the handle member via respective lead blocks fixed to the stationary and movable housings; and thereby realizing electrical connection means for providing a heater circuit device for steering apparatus, an air bag system, a horn circuit and/or the like for motor vehicle, with an electrical connection.
That is, the electrical connection means functions when a predetermined current flows through each of a plurality of conductors of the flexible cables.
However, in the above-described rotary connector, the flexible cable is accommodated in a space formed between the stationary housing and the movable housing and is constructed so that a plurality of conductors made of a strip of extremely thin copper (Cu) foil or the like are stuck to the insulating films. As a result, the amount of current allowed to flow through each conductor cannot be made larger than expected.
Additionally, in recent years, it has been seen a phenomenon as a trend that a vehicle primarily used in a cold district is equipped with a steering apparatus constructed such that a heater circuit device to warm a steering (handle) is incorporated therein. The heater circuit device used for the steering is required to supply a relatively large current to a heater device to generate heat therein and therefore, it has been required that the conductor of the flexible cable is able to allow a large current to flow therethrough.
However, when a large current flows through the conductor, such a problem has been seen that the conductor generates excessive heat in some cases and owing to the increase in temperature of the conductor caused by this excessive heat generation, the insulating film is deformed, molten adhesively or the conductor is broken, leading to occurrence of trouble in the function of rotary connector.
An object of the present invention is to provide a rotary connector capable of preventing excessive temperature increase generated in a flexible cable by employing temperature detection means for detecting the temperature of the flexible cable.
A rotary connector of the present invention comprises:
a stationary housing having a cylindrical portion;
a movable housing having a cylindrical portion and provided on the stationary housing so as to be rotatable relatively thereto; and
a flexible cable accommodated within a housing section formed between the stationary housing and the movable housing;
in which the flexible cable is constructed such that both ends thereof are fixed to the stationary housing and the movable housing, respectively, and the rotary connector is further constructed to have temperature detection means therein for detecting a temperature of the flexible cable in a state of the temperature detection means being exposed within the housing section.
The above-described construction allows the rotary connector to monitor the increase in temperature of the flexible cable due to the current flow therethrough and therefore, the rotary connector is able to detect the increase in temperature of the flexible cable due to the excessive heat generation via the temperature detection means and further appropriately control the excessive heat generation in the flexible cable by receiving a signal from the temperature detection means, thereby realizing provision of a rotary connector capable of preventing deformation or fusion of insulating film.
Furthermore, the rotary connector of the present invention is further constructed such that the temperature detection means is provided in one of the cylindrical portion of the stationary housing and the cylindrical portion of the movable housing.
The above-described construction can prevent the occurrence of phenomenon that the rotary connector becomes large by installation of the temperature detection means and further facilitate the installation thereof.
Additionally, the rotary connector of the present invention further includes a holding member therein for holding the temperature detection means and the holding member is provided in one of the cylindrical portion of the stationary housing and the cylindrical portion of the movable housing.
The above-described construction allows for installation of the temperature detection means via the holding member, thereby enhancing easiness of installation and removal of the temperature detection means.
Moreover, the rotary connector of the present invention is further constructed such that the temperature detection means is provided near one of fixing portions located between the flexible cable and one of the stationary housing and the movable housing.
The above-described construction allows for stable operation for detecting temperature via the temperature detection means since the flexible cable moves little near the lead blocks in the event of the flexible cable being wound or unwound.
In addition, the rotary connector of the present invention further includes a pressing member therein provided to face the temperature detection means and press the flexible cable against the temperature detection means.
The above-described construction allows for secure operation for detecting the temperature of the flexible cable via the temperature detection means since the flexible cable is pressed against the temperature detection means by the pressing member.
Furthermore, the rotary connector of the present invention is further constructed such that the pressing member has a structure independent of the stationary housing and the movable housing and is provided in one of the cylindrical portion of the stationary housing and the cylindrical portion of the movable housing.
Compared with the case where the stationary or movable housing itself is directly installed in the rotary connector to replace associated pressing member, the above-described construction allows the operation for installing and replacing the pressing member to become easier and lower in cost since the pressing member has a structure independent of the housing.
Moreover, the rotary connector of the present invention is further constructed such that the pressing member includes an elastic portion therein having elasticity and presses the flexible cable via the elastic portion.
The above-described construction allows the rotary connector to further securely press the flexible cable against the temperature detection means via the pressing member.
Additionally, the rotary connector of the present invention is further constructed such that the temperature detection means is composed of a temperature sensor.
The above-described construction allows for provision of a low-cost and performance-stable rotary connector since the temperature sensor is inexpensive and is able to easily detect the desired temperature.
Furthermore, the rotary connector of the present invention is further constructed such that the temperature detection means is composed of a thermistor.
The above-described construction allows for provision of a compact and inexpensive rotary connector since the thermistor is inexpensive in addition to being compact.